Metal spraying apparatus



April 16, 1968 w. E. STANTON 3,378,203

METAL SPRAYING APPARATUS Filed Feb. 21, 1966 4 Sheets-Sheet. 1

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ow siani'on Fig. Limb E63 United States Patent 3,378,203 METAL SPRAYING APPARATUS Wilfred Edgar Stanton, Sedgley, Dudley, England, as-

signor to Metallisation Limited, Birmingham, England, a British company Filed Feb. 21, 1966, Ser. No. 529,140 Claims priority, application Great Britain, Feb. 25, 1965, 8,102/ 65 5 Claims. (Cl. 239-84) ABSTRACT OF THE DISCLOSURE A metal spraying apparatus in which a metallic wire is fed through a bore in a nozzle assembly in which a flame acts upon and melts the wire and in which a jetof compressed air is so directed relative to the wire" and the flame to propel a stream of molten droplets from the nozzle, there being a restricted passage leading to the bore from the air supply for the air jet to create a pressure in the bore suflicient only to prevent the flame spreading back into the bore, and a further passage connecting the bore with an auxiliary air supply which when operative supplies sufficient air to the bore to cause a layer of air to be formed around the wire in the nozzle to separate the wire from the flame.

This invention relates to metal spraying apparatus (hereinafter referred to as being of the kind specified) in which a metallic wire or rod (hereinafter for convenience referred to as Wire) is fed by a wire feeding means through a bore in a nozzle assembly in which a flame acts upon and melts the wire, and in which a stream of compressed air or other non-combustible gas (hereinafter referred to for convenience as the air jet) is so directed relative to the wire and the flame that molten metal droplets from the wire are propelled into a stream.

It will be appreciated that the air jet serves to impart a high velocity to the flame by way of frictional contact with the gases undergoing combustion, and the air and gaesous combustion products together entrain and propel the metal droplets.

The flame is normally produced by combuston of a suitable gaseous fuel mixture, such as a mixture of oxygen and either acetlyene or pro-pane. The flame is normally of annular form and is surrounded by the air jet, which is of conical form. The air jet may also assist in cooling the nozzle parts.

In met-a1 spraying apparatus of the kind specified, the gaseous fuel mixture may be fed through drilled or fluted channels in the nozzle to emerge from a plurality of burner ports arranged in a circle around the bore through which the wire is fed. The channels may be inclined such that the streams of gaseous fuel mixture issuing from the ports converge to a point axially in line with the wire downstream of the nozzle in the direction of feed of the wire.

The convergence of the streams of fuel together with the thermal expansion of the gaseous combustion products results in a back pressure being exerted in opposition to the forward direction of flow of the gases. This has the effect of causing a portion of the flame to impinge against the front face of the nozzle, from which position it may spread rearwardly into the nozzle along the clearance space between the wire and the bore of the nozzle. With such an arrangement under these circumstances sutlicient heat may be conveyed to the wire to bring about fusion and incipient welding of the wire to the nozzle, thereby obstructing the normal infeed of Wire. This problem is particularly acute when the metal being sprayed has a low melting point, for example, tin or zinc.

Furthermore, such impingement of the flame against the front face of the nozzle and rearward spread of the flame along the clearance space as aforesaid may take place if, for any reason, the feeding of the wire is interrupted. The likelihood of the incipient welding of the wire to the nozzle is greater when the wire is stationary within the bore of the nozzle, than when the wire is in motion. Such fusion and incipient welding of the wire may prevent feed of the wire through the bore when subsequently required and thus, such apparatus suffers from the disadvantage that intermittent metal spraying operations are not practicable, unless the flame is extinguished when actual spraying and wire feed ceases.

In some cases, it is advantageous to be able to interrupt the wire feed while the flame is allowed to continue burning. One example is in the use of automatic spraying apparatus when it is required that certain areas of members undergoing the spray coating treatment should remain uncoated. Masks are sometimes used to protect such uncoated areas but such masks are costly to make and much time is consumed in attaching them to the members in the required positions. Furthermore, the exposed surfaces of the masks become coated with the sprayed deposit, and this entails wast-age of spraying material and consumption of time for cleaning the masks before they are re-used.

A further example in which it is advantageous to halt the wire feed is in the manual spray coating of members of similar size or shape which arrive at the spraying station in repetitive quantities. In such a case spraying time is lost during the periods while each complete sprayed member is being replaced by a further member ready for spraying. It is not always convenient to shut off the apparatus by extinguishing the flame yet it is extremely wasteful to allow rod to be consumed and the spray to continue to be emitted from the apparatus even during such short intervals.

It is known that flame impingement at the nozzle face can be reduced with consequent reduction of the likelihood of incipient welding of the wire 'by decreasing the angle at which the channels converge, so that the focal point of the fuel streams occurs further downstream from the normal melting zone. The effect in this case is to allow more freedom for the gaseous fuel to expand as it flows downstream and this tends to cause the production of a hollow flame of somewhat greater length than is normally used.

Such an arrangement suffers from the disadvantage that, if the included angle between the channels is less than about 15 degrees, the rate at which heat is transferred to the rod becomes reduced. Consequently such spraying apparatus cannot be operated at a high level of efficiency. Furthermore, the force exerted on the molten wire due to the impingement of the gases undergoing combustion is reduced, since a shallower angle of approach gives rise to an increased area of impingement with the result that the gases do not so effectively propel the molten material into the spray stream. Enlarged droplets are thus produced leading to the production of deposits of coarse texture and inferior mechanical strength.

It is an object of the present invention to overcome or reduce these disadvantages.

According to the present invention we provide metal spraying apparatus of the kind specified wherein a passageway system in the apparatus for the delivery of compressed air is so formed or arranged as to deliver a quantity of the air in a forward direction into a zone between the wire and the flame adjacent to the front face of the nozzle.

With the arrangement according to the invention the delivery of compressed'air (which term is to be deemed -8 to include any other non-combustible gas) serves to raise the pressure within said zone to a value sufficient to balance the back pressure exerted by the combustion gases and reduce impingement of the flame on the nozzle face so as to prevent, or at least substantially reduce the chances of, incipient Welding as aforesaid when the wire is in motion.

Preferably, means are provided for supplementing said quantity when the normal forward rate of feed of the wire is not maintained. The supplementary quantity of compressed air which is introduced in this case when the rate of feed of the wire is reduced, and particularly when the wire is stationary, creates an excess of pressure within said zone, with the result that air flows to the core of the flame from said zone and forms a relatively cool layer around the wire, which is thereby shielded from the flame.

Apparatus according to the invention is preferably provided with means for stopping and starting the feed of the wire at will, said means being operatively associated with said means for supplementing the quantity of com pressed air delivered, so that said supplementary quantity is introduced into said zone whilst the wire is stationary and is cut off from said zone whilst the wire is in motion.

In a preferred embodiment according to the invention, said means for supplementing the supply of compressed air comprises a manually operable pneumatic control valve which has an inlet coupled to a source of compressed air, and two outlets to which said compressed air may be selectively supplied, the first of which outlets is connected to the passageway system for the supply of compressed air to said zone, and the second of which outlets is connected to means for controlling operation of the wire feeding means, so that when the second of said outlet means is selected, the wire is fed forwardly and the supplementary air supply is shut off, and when the first of said outlet means is selected, the wire feeding means is inoperative and the supplementary air is supplied to said zone. Said passageway system may include two inlets for compressed air, one of said inlets being connected to a duct system supplying compressed air for said air jet, and the other of said inlets being connected to said pneumatic control valve.

In this way a continuous supply of compressed air is provided for said zone by bleeding off a portion of the compressed air supplied to the air jet associated with the flame through a connecting passageway or bleed aperture provided in the apparatus which connects said air jet supply duct with said passageway system. Preferably, said passageway system is arranged to supply compressed air to said bore through which the wire is fed.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 shows a plan view of a hand-held metal spraying gun,

FIGURE 2 shows the gun in side elevation,

FIGURE 3 shows the gun in front elevation,

FIGURE 4 shows a longitudinal cross section on the line IVIV of FIGURE 3 through a nozzle assembly,

FIGURE 5 shows a cross section on the line VV of FIGURE 4,

FIGURE 6 shows a cross section on the line VI-VI of FIGURE 4,

FIGURE 7 shows a cross section on the line VII-VII of FIGURE 4,

FIGURE 8 shows a wire feed assembly in front view and an associated wire feed control device in section on the line VIIIVIII of FIGURE 1,

FIGURE 9 shows a longitudinal cross section on the line IX-IX of FIGURES 1 and 8,

FIGURE 10 shows a transverse cross section through a control valve on the line XX of FIGURE 2 and 11,

FIGURE 11 shows a section on the line XI-XI of FIGURE 9,

FIGURE 12 shows a cross section on the line XII-XII of FIGURE 1 through a pawl device for preventing reverse movement of the wire, and

FIGURE 13 shows schematically gas, oxygen and air supply systems and the mechanism for feeding the wire.

The apparatus illustrated is a hand-held spray gun, although it will be appreciated that the invention may be applied to a gun forming part of an automated machine and operated by remote control.

The gun comprises a nozzle assembly 10, a wire feed-- ing means 11 behind the nozzle assembly, a wire feed control means 12, to one side of the wire feeding means, a wire drive means comprising a motor 13 driven by compressed air and disposed to the rear of the wire feeding means, a co-ordinating means comprising a control valve 14 disposed beneath the wire drive motor, a master valve 15 disposed beneath the nozzle assembly, and a pawl device 16 mounted to the rear of the wire feed motor to prevent reverse movement of the wire 19. All the above mentioned parts 10 to 16, are supported on a base 17 provided with a hand grip 18.

Referring firstly to FIGURES 4 to 7, the nozzle assembly 10 comprises a plate-like supporting head 21 formed at one end (normally the end which is uppermost when the gun is in use, and herein all directional references are given with reference to the gun in such posi tion) with an annular sleeve 22 extending forwardly. C0- axial with the sleeve 22, a bore 23 is formed through the head 21 and a sheath 24 is mounted co-axially within the bore by means of an annular boss 25 on the sheath. The bore 26 of the sheath 24 forms a guide for the wire 19 and the rear end of the sheath is formed with a bush 27 through which the wire passes as a close but easy sliding fit.

The forward face 28 of the head 21 within the area of the sleeve 22 is surrounded by two annular stepped portions 29 and 3t] and the inner face 31 of the sleeve 22 is threaded to receive a further sleeve hereinafter described. Within the sleeve 22 there is located a generally cylindrical mixing block 32 made of light alloy, which over most of its length has a diameter equal to that of the face 28, the rear end of the mixing block 32 being located Within the inner annular stepped portion 29. The mixing block 32 is formed with a radial projection extending axially from approximately mid-way along the length of the block 32 almost to the rear end thereof. The spacing between the rear face 34 of the projection 33 and the rear face 35 of the mixing block itself is such that these faces respectively abut the forward face of the stepped portion 29 and the forward face 28 of the head 21.

At its forward end, the mixing block 32 is formed with two portions 36 and 37 of respectively decreased radius, and the sheath 24 is received in a central bore 38 extending through the mixing block 32, the forward end of the sheath 24 being flush with that of the mixing block.

The stem 42 fits closely into the forward portion 43 of the axial bore through the nozzle and is of slightly increased diameter over the rear half of its length, the axial bore being widened over the rear part of the forward portion of the stem 42 to provide a clearance 44 and further widened over the rear portion of the stem 42 to extend said clearance over the rear portion of the stem as at 45. The rear end of the stem 42 is formed with a head 46 of enlarged diameter which is an accurate fit in a counterbored portion 47 of the axial bore. The stem 42 itself has over most of its length an internal diameter appreciably greater than the diameter of the wire 19, but is of reduced diameter internally at its forward end so that there is only a very slight clearance 48 between the wire and the stem where the former issues from the front face of the nozzle.

The mixing block and nozzle are held in the sleeve 22 by means of a further sleeve 49 which is screwed therein. Approximately half-Way along its length the sleeve 49 carries a spacing washer 52 in which the cylindrical portion 40 of the nozzle 39 is held. The sleeve 49 is, throughout its length, of greater internal diameter than the external diameter of the mixing block and nozzle so as to define annular chambers 50 and 51 respectively around these parts and separated by the washer 52, which latter is provided with apertures 53 so that the chambers 50 and 51 communicate with each other.

The nozzle assembly is completed by a cone 54 which surrounds the nozzle 39 and is held in place by a lock ring 55 screwed into the forward end of the sleeve 49. The lock ring 55 is formed so as to provide a clearance 56 around the rear end of the cone and the latter is seated in an annular groove 57 formed in the nozzle 39 so that there is a clearance 58 between the inner surface of the cone 54 and the outer surface of the nozzle 39.

The clearances 44, 45, 48 and 56, 58 together with chambers 50, 51 form part of passageway systems in the nozzle assembly. These systems are completed by the bores now described. In the supporting head 21 there are provided three main bores 60, 61 and 62 which extend upwardly from the master valve 15, the latter incorporating three cam operated diaphragm valves and three inlet unions respectively for oxygen, a combustible gas such as acetylene or propane, and compressed air. At its lower end the main bore 62 for compressed air is of approximately twice the diameter of the other main bores 60 and 61. A horizontally, rearwardly extending bore 63 leads from the wide part of the main bore 62 to supply compressed air to the motor 13.

At its upper end the main bore 62 intercepts seven horizontally extending bores 64 leading to and spaced circumferentially around the outer stepped portion 30 of the head. These bores 64 enable compressed air to flow into the chambers 50 and 51 and thence through a plurality of bores 65 which extend inwardly through the rear end portion of the cone 54 to the clearance space 58 so as to emerge as a conical air jet A within the cone. These bores, chambers and clearance spaces together constitute a first passageway system forming a primary air supply means.

The central, gas carrying, main bore 61 intercepts three fine horizontal bores 66 which communicate with an annular cavity 71 defined by the side of the inner stepped portion 29, outer margin of face 28 and a recess around the rear end of the mixing block 32. In register with this cavity 71 the mixing block is formed with a plurality of forwardly extending, inwardly inclined bores 72 which open out into wider axial bores forming mixing chambers 69 in the block 32.

The remaining, oxygen carrying, main bore 60 in the supporting head 21 intercepts four horizontal bores 70 which lead to an annular recess 67 formed in the face 28 of the head 21, A plurality of forwardly directed bores 68 lead to the mixing chambers 69 where the gas and oxygen flows meet and mix.

The mixing chambers 69 terminate in an annular recess 73 in the forward face of the mixing block 32, and the nozzle 39 is formed with a plurality of bores 74 which are inwardly inclined towards the wire at a minimum included angle of a typical value being The bores 74 register at their rear ends with the annular recess 73 and emerge at burner ports in the front face 75 of the nozzle 39, the forward parts of these bores being of somewhat reduced diameter as compared with their rear parts.

Thus, air and gas is conveyed to the burner ports through a system of bores and chambers, etc., which together form a gas supply means to form flame B which is directed on to the wire, the outer cone or air jet A comprising air delivered from around the nozzle serving to accelerate and direct the flame on to the wire. In order to overcome any tendency of the back pressure to cause the flame to spread into the clearance space 48 around the wire, radial bores 76 are formed in the nozzle 49 to extend between the chamber 51 and the clearance around the stem 42. The latter is also formed with a radial bore 78 to admit air to the interior of the stem. In this way a proportion of compressed air is bled from chamber 51, through a second passageway system comprising bores 76, clearances 45 and 44, bore 78 and clearance 48 forming a secondary air supply means, to balance the back pressure and prevent the flame spreading into the clearance 48. This arrangement is preferred since the respective total cross sectional areas of the bores 65 and bores 76 can be so arranged that the air pressure applied at the clearance 48 just balances the back pressure due to the flame without causing any substantial amount of cold air to actually flow into the centre of the flame to cool the latter. However, it will be possible to achieve a similar effect by conveying such air to a plurality of fine ports arranged around the wire between the latter and the burner ports. In such case it will be necessary to ensure that the air flow is restricted to such an extent that the flame is not appreciably cooled but that the supply of air establishes a zone of pressure around the wire where it emerges from the nozzle to counteract the back pressure of the flame.

Such supply of air to balance the back pressure of the flame can be adjusted by experiment to be just sufficient to overcome the problems of incipient welding previously mentioned when the wire is being fed forwardly at a normal rate. However, it is preferred to provide additional means to augment the supply of compressed air through the clearance 48 when forward feed of the wire is arrested, since in this case the rate of conduction of heat rearwardly to the part of the wire temporarily located in the stem 42 would otherwise rapidly raise the temperature of the wire to such an extent for there to be a danger of incipient welding.

For this purpose a bore 79 is formed to extend downwardly from the top of the supporting head 21, this bore being widened at its outer end to receive a coupling 81). At its lower end the bore 79 opens into the bore 23, in which the sheath 24 is supported, in register with an annular recess 31 formed in the boss 25 on the sheath. Two small radial bores 82 extend from the recess 81 to the bore 26 within the sheath so that compressed air can flow from the coupling through a third passageway system comprising bore 79, recess 81, bores 82 and bore 26 of the sheath 24, which form an auxiliary air supply means from which air passes through the stem 42 to emerge, together with that from the secondary air supply means, from the clearance 48 arounid the wire at a front face of the nozzle 39. In this way an additional quantity of air is supplied to supplement that flowing to the clearance 48 via the radial bores 76 in the nozzle 39.

The supply of this additional quantity of air via coupling 84 is controlled by the three-way valve 14 which supplies air either to the nozzle assembly 10 or to the control device 12, The valve 14 is shown in FIGURES 9 and 10 and comprises a block-like body provided with two recesses 91 and 92 for outlet connectors on one side and a single recess 93 for an inlet connector on the other side. Each of these recesses has opening into their respective inner ends an axial bore 94 which intercepts a respective bore 95 leading to the rearwardly presented surface of the body. A cover piece 96 is secured to the body 90 at the rear surface thereof and houses a sliding element 97 which is movable, by means of a button 98 projecting through slot 99 in the cover piece, so as selectively to bring the inlet into communication with either of the outlets. It will be noted that the sliding element 97 is so dimensioned that when the inlet is in communication with one outlet, the other outlet is open to the amosphere via the slot in the cover piece.

The inlet of the valve 14 is connected by a tube 100 which includes a shut-off valve 109 to a main compressed air supply line 101 which leads from a source of compressed air (not shown) to an air inlet 102 on the master valve 15 at the underside of the nozzle assembly 10. One of the outlets of the valve 14 is connected by tube 10-3 to the coupling St! on top of the nozzle assembly 10 whilst the other outlet is connected by tube 144 to an inlet union 7 105 on the control device 12, the function and construction of which is now explained.

The control device 12 comprises a housing formed by two generally cup-shaped end members 110 spaced apart by a ring 111. Two resiliently deformable diaphragms 112a and 112b are clamped between the end members and respective sides of the ring 111 to define a chamber 113 to which compressed air can be supplied by way of a port 114 in which the union 105 is situated.

Each diaphragm carries on its outer face a plate 115 of a diameter slightly less than the internal diameter of the housing, and secured by means of screws passing through the diaphragm into a small plate 117 disposed centrally on the inner side of the diaphragm.

The plate 115 attached to the diaphragm 11211 has secured thereto one end of a tie bar formed by a tube 118 which projects outwardly of the housing through an apertured boss 120. A tie rod 119 is disposed within the tube 118 and projects through an aperture in the diaphragm 112k and is secured to the smaller plate 117 attached to the other diaphragm 112a.

The arrangement is such that when the sliding element of the valve 14 is set to supply compressed air to the chamber 113, the diaphragms are urged apart against the force of springs 116 which act between the plates 118 and the inner surfaces of the end members 110. In this way the tube 118 moves in one direction (to the right in FIGURE 8) whilst the rod 119 moves in the opposite direction. When the sliding element of the valve is moved to its other position the compressed air in the chamber 113 is released and the tube and rod revert to their illustrated positions under the influence of the springs 116.

The control device 12 is attached by the boss 120 to a casing 121 which partially encloses the wire feed assembly 11 and the tube 118 and rod 119 extend through the boss 120 into the casing and are operatively connected to the wire feed means as hereinafter described.

The wire is driven forwardly into the nozzle assembly by the compressed airmotor 13. The air supply for this is from the bore 63 previously mentioned. The motor is of generally conventional form and has a transverse output shaft 130 provided with a centrally disposed worm gear 131 which meshes with a secondary gear 132 carried at the rear end of a forwardly extending drive shaft 133. This drive shaft is mounted at its rear end in a bearing 134 mounted in the rear wall of the motor casing and at its forward end in a bearing 135 mounted in the front wall of the casing 121. Over the forward half of its length the drive shaft 133 is formed with a worm gear 136 which meshes with two oppositely disposed pinions 137 mounted on generally vertically arranged shafts 138 which carry at their upper ends wire driving rollers 139 having a milled or otherwise roughened wireengaging surface 140.

Each shaft 138 is supported in two vertically spaced bearing lugs 141 respectively formed on two cross pieces 142 extending between two horizontally spaced bearing rings 143. Thus there are four such rings 143 in all, the inner pair supporting the right-hand drive roller 139 as seen in FIGURE 8 and the outer pair supporting the left-hand drive roller. The bearing rings 143 are rotatably carried by a yoke 144 which is supported in the manner of a cantilever at the forward end by the front wall of the casing 121 and which in turn carries the bearing 135 for the drive shaft 133. The yoke 144 is bifurcated so as to be open laterally to enable the pinions 137 to mesh with the worm gear 136.

In this way, the drive rollers 139 can be moved laterally into and out of engagement with the wire 19 by rotation of the support assembly comprising rings 143, cross pieces 142 and lugs 141 about the yoke 144 and the drive shaft 133. This is achieved by the opposed movement of the tube 118 and rod 119 of the control device 12 previously described. The tube 118 abuts a lug 14-5 projecting radially from the outer forward ring 143 whilst the rod 119 extends through an aperture in this lug and is connected to a lug 146 which projects forwardly from the upper cross piece where the latter joins the inner forward ring 143. A spring 147 is supported on the rod 119 and acts between the lugs 145 and 146 so as to urge them, and consequently the drive rollers 139, apart.

Thus, when the valve 14 is set to supply air to the chamber 113 of the control device 12, the tube 118 is moved to the right as seen in FIGURE 8, and the rod 119 is moved to the left, in the manner previously explained, so that the rollers 139 are moved together to engage the wire 19 and drive it forwardly. When the valve 14 is reset to supply air to the coupling 80 on the nozzle assembly 10, the chamber 113 is open to the atmosphere and the springs 116 and 147 cause the rollers 139 to move apart.

In this way the supply of an additional quantity of compressed air to the nozzle is controlled in accordance with the movement of the Wire, so that when forward feed of the wire is stopped, additional air is supplied to the clearance 48 so as to cause a zone C of cool air to be formed around the wire projecting from the nozzle, this in turn being surrounded by the hot zone B of the flame and the air jet A as seen in FIGURE 4.

The apparatus is also provided with a device 16 for preventing reverse movement of the wire when the drive rollers 139 are in their inoperative position. The device 16 comprises a supporting roller 150 and a pawl 151 mounted in a block 152 attached to the rear of the casing of the motor 13. The wire 19 is fed between the roller 150 and pawl 151 and through a tubular wire guide 153, the pawl being urged towards the Wire by a leaf spring 154. Any rearward movement of the wire causes the pawl to grip the latter. When it is required to change the metal being sprayed or the gauge of the wire being used, the wire can be withdrawn by temporarily displacing the pawl 151 away from the wire by means of a projection 155 formed on the pawl for this purpose.

The overall scheme of the various passageways of the oxygen, gas, and air supply systems, together with the mechanical connections of the apparatus is shown in FIGURE 13. Here:

The arrow D represents the flow of oxygen through 60, 70 and 67, 68 to the mixing chamber 69;

The arrow E represents the flow of gas through 61, 66, 71 and 72 to the mixing chambers;

The arrow F represents the flow of mixed oxygen and gas from the chamber 69 via 74 to the flame B;

The arrow G represents tht flow of compressed air through 62, 64, 50, 51, 56, 65, and 58 to the air jet A;

The arrow H represents the flow of compressed air bled from the flow G through 76, 45, 44, 78, 48 to the zone C; and

The arrow I represents the flow of additional compressed air to the zone C when the wire is not being driven forward, through 80, 79, 81, 82, 26, and 48.

It will be appreciated that although in the preferred embodiment described some compressed air is always supplied to the space around the wire where it emerges from the nozzle, and the quantity of air is increased when the wire is stationary, the quantity of cool air delivered into zone C whilst the wire is being fed for wardly is quite small and consequently zone C itself is small and the temperature of the flame is substantially unaffected. However, it would be possible for the compressed air to be supplied to this zone only whilst the wire is stationary and not while the wire is being fed forwardly under circumstances that make it unnecessary to supply compressed air to this zone at this time.

What I claim then is:

1. In metal spraying apparatus comprising:

(a) a nozzle assembly having a front face, a bore, and

burner ports arranged around said bore, said bore and said burner ports opening into said front face,

(b) wire feeding means for feeding a metal Wire, when the apparatus is in use, through said bore of said nozzle assembly,

(c) gas supply means for supplying a combustible gaseous mixture to said burner ports and producing a flame around and directed onto said wire to melt the latter and produce molten droplets of metal,

(d) primary air supply means for supplying compressed air around the flame to form an air jet to propel said droplets into a steam, the improvement comprising:

(e) secondary air supply means for supplying a quantity of compressed air to said bore sufiicient only to prevent said flame spreading into said bore, and

(f) auxiliary air supply means for supplying a supplementary quantity of compressed air to a zone adjacent to said front face of said nozzle assembly and immediately next to said wire between the latter and the flame to surround said wire and separate the latter from said flame by a layer of air.

2. Metal spraying apparatus as claimed in claim 1,

further comprising:

(a) Wire feed control means for starting and stopping at will the feeding of said wire through said bore of said nozzle assembly by said wire feeding means, and

(b) co-ordinating means operatively associated with said auxiliary air supply means and said wire feed control means to cause said supplementary quantity of compressed air to be supplied to said zone Whilst said wire is stationary and to cause said supply of supplementary quantity of compressed air to be cutoff whilst said wire is being fed through said bore of said nozzle assembly by said wire feeding means.

3. Metal spraying apparatus as claimed in claim 2 wherein:

(a) said Wire feeding means comprises a pair of rollers, means for driving said rollers, and bearing means for each roller, said bearing means being movable under the control of said wire feed control means between an operative position in which said rollers engage and drive said wire, when the apparatus is in use, and an inoperative position in which said rollers are disengaged from said Wire,

(b) said Wire feed control means comprises a chamber, two relatively movable members disposed within said chamber and which are movable to eitect movement of said bearing means to their inoperative position upon admission of compressed air to said chamber, and means establishing operative connection between said relatively movable members and said bearing members, and

(c) said co-ordinating means comprises a pneumatic control valve having an inlet for connection to a source of compressed air, a first outlet connected to said auxiliary air supply means, a second outlet connected to said chamber of said wire feed control means, and means for selectively placing said inlet in communication with either of said outlets.

4. Metal spraying apparatus as claimed in claim 3 wherein:

(a) said primary air supply means comprises a first passageway system in said nozzle assembly,

(b) said secondary air supply means comprises a second passageway system in said nozzle assembly branching from said first passageway system, and

(c) said auxiliary air supply means comprises a third passageway system joining said second passageway system.

5. Metal spraying apparatus as claimed in claim 4 wherein said second and third passageway systems re- 3 spectively supply said quantity and supplementary quantity of compressed air to said bore of said nozzle assembly.

References Cited UNITED STATES PATENTS 2,268,202 12/1941 Britten 23984 2,973,892 3/1961 Hedde 226-l87X ALLEN N. KNOWLES, Primary Examiner.

M. HENSON WOOD, JR., Examiner.

l-I. NATTER, Assistant Examiner. 

